Design, simulation and experimental study of shape memory alloy and micro-motor activated high pressure optical cell for bio-physical studies

Abstract

During the past two decades, bio-physicists have had an increasing interest in finding out what happens when two bio-material solutions are mixed under high pressure. Compared to temperature, pressure makes more contributions to our fundamental understanding of the structure-function relationship of biological systems, because pressure produces only volume changes under isothermal conditions, and pressure results can then be interpreted in a more straightforward manner. As pressure brings molecules closer and thus enhances intermolecular interactions, the previously unattainable properties of biological molecules may be discovered by using high-pressure optical cells (HPOC) technology.Window-type HPOC such as the one designed by Paladini and Weber have provided biophysicists with a powerful tool to understanding the structure-function relationships of biological molecules. However, the conventional HPOC is only good for single solution testing and does not allow for quick mixing and stirring of additional components while the specimen is under pressure. To mix two solutions under pressure, Zhou and Chong developed a laser activated dual chamber HPOC. However, the expensive laser device and its unavailability in most laboratories make the application difficult. Zhou and Chong also introduced shape memory alloy (SMA) as an actuator to unplug a urethane stopper with a biasing spring for agitation. The drawback of the biasing spring is that the spring blocks the observing light beam and creates the creation of unwanted reflections, and the SMA spring actuator method has never been put to practice.To thoroughly study the feasibility of SMA as an actuator, five types of SMA actuators were designed, simulated and tested for unplugging and mixing purposes. To conduct this research, SMA helical springs were fabricated in house according to the design requirements. With different combinations of SMA tensile springs, SMA compressive spring and biasing spring, significant ranges of vibration were developed. To further improving mixing process, a unique hybrid design of SMA as an actuator to unplug the stopper and micro-motor as a stir device to agitate the solutions was developed. Rapid mixing of 95% of total solution in 10 seconds was achieved under 300 bars. A new HPOC was designed according to the new cuvette with its new unplug and mixing mechanism. Our industrial partner, ISS, further modified our design for easy manufacturing reason and fabricated the HPOC which made SMA actuator mixing test under pressure possible. Since the inside chamber height was increased to accommodate the new cuvette and electrical leads were introduced through the cell body to achieve remote control outside of the HPOC, FEA Method was used to assure the HPOC’s safety under high pressure. Since the device is designed for bio-physical study, bio-compatibility of Nitinol SMA with protein and phospholipids was studied. As SMA actuator generates heat to function, heat transfer simulation was conducted to understand the heat influence. The enzyme…